In recent years, such portable wireless devices as portable telephones, PHS and the like are widely in use. These devices are equipped with an antenna for receiving and transmitting radio waves. This antenna is formed of a first antenna element that is made operative when the antenna is extended and a second antenna element that is made operative when the antenna is retracted into the wireless device's case for the convenience of portability.
A conventional type of the antenna as mentioned above will be described in the following with reference to FIG. 7 and FIG. 8:
FIG. 7 is a cross-sectional view of a prior art antenna.
In FIG. 7, the bottom end of a first antenna element 1 is coupled with a stopper 3 formed of an electrically conductive metal and the upper part of the first antenna element 1 is fixed to a cylindrical column like joint 4 formed of an insulating resin and provided with screw threads 4A around the periphery of its top end. In addition, a tube 2 formed of an insulating resin is used to cover the periphery of the first antenna element 1. The first antenna element 1 is formed of a linear metallic round wire.
A second antenna element 5 is formed of such an electrically conductive metal as copper, copper alloy or the like and structured like a coil winding. The second antenna element 5 is wound around a bobbin 6 formed of an insulating resin.
A feeding fixture 7 is formed of an electrically conductive metal.
The bottom end of the second antenna element 5 is attached to the top end of the feeding fixture 7 by winding around it, thereby completing an electrical connection therebetween.
A cover 8 formed of an insulating resin covers the periphery of the second antenna element 5. Screw threads 7A are formed inside of the bottom end of the feeding fixture 7 and the screw threads 4A of the joint 4 are screwed into the screw threads 7A with an adhesive applied for the prevention of loosening of the joint 4 due to its rotation.
An antenna insertion hole 9A and a spring insertion hole 9B are formed in the center of an antenna holder 9. Springs 10 contained in the spring insertion hole 9B are pressed against the stopper 3, which is coupled with the first antenna element 1, and kept parallel in position with the axis line of the stopper 3 by a spring action. A feeding nut 11 connected with electric circuits (not shown in FIG. 7) of a wireless device is tightened to screw threads 9C formed around the periphery of an antenna holder 9. The antenna holder 9 is fixed to the case 12 of the wireless device. The antenna holder 9 is formed of an electrically conductive metal. The springs 10 are also formed of an electrically conductive metal.
When the antenna is extended as shown in FIG. 7, the stopper 3 is brought into contact with the springs 10 contained in the antenna holder 9, which is attached to the case 12 of the wireless device, thereby enabling the first antenna element 1 connected electrically with the feeding nut 11 to transmit/receive radio waves via the antenna.
When the first antenna element 1 is retracted in the case 12 of the wireless device as shown in FIG. 8, the stopper 3 coupled with the first antenna element 1 is separated from the antenna holder 9 and the feeding fixture 7 is brought into contact with the springs 10 contained in the antenna holder 9, thereby enabling the second antenna element 5 connected electrically with the feeding nut 11 via the feeding fixture 7 to transmit/receive radio waves via the antenna.
However, since with the foregoing prior art antenna the coupling between the joint 4 fixed to the first antenna element 1 and the feeding fixture 7 connected with the second antenna element 5 is performed by screwing the screw threads 4A of the joint 4 into the screw threads 7A of the feeding fixture 7 with an adhesive applied thereto the cost of the molding process involved with the screw threads 4A of the joint 4 tends to become high and also the processing cost involved with cutting the screw threads 7A of the feeding fixture 7 and the like becomes expensive. Furthermore, controlling the position where an adhesive is applied and the amount of the adhesive applied between the screw threads 4A and the screw threads 7A is rather difficult.
In addition, the assembly work of the antenna is time consuming.
The present invention provides an antenna that facilitates the preparations of piece parts required in coupling the joint and the feeding fixture together and also the assembly work involved, resulting in less expense in time and effort and leading to realization of a less expensive antenna.